Dry spinning process

Dry Spinning. On a worldwide basis, about 90% of all spandex fibers are produced by various adaptations of dry spinning (15,16). The solution dry spinning process is illustrated in Figure 5. The polymer spinning solution is metered at a constant temperature by a precision gear pump... 

One report (13) describes the procedure for spinning dry asymmetric ceUulose acetate fiber with a bore skin. Such fibers are spun in a modified dry-spinning process in which a volatile Uquid (methyl formate) is used as the ceUulose acetate solvent. The bore coagulating Uquid is isopropyl alcohol, which is subsequentiy removed. The advantages of these dry fibers over most ceUulose acetate membranes are that they can be stored dry, they are wet-dry reversible, they can be sterilized and packed dry, and they are ready for use without removal of preservatives. 

A variation on the wet-spinning technique involves extruding into a heated gas environment. In this dry-spinning process, the temperature and composition of the gas control the extraction process. 

Rayon was first made by denitration of cellulose fibers (Chardonnet process). The cellulose was first reacted with a mixt of nitric and sulfuric acids to form NC, The prod was then dissolved in a mixt of eth and ethanol and spun into yarn by a "dry spinning process. In some instances the yarn was denitrated by alkaline hydrosulfites, neutralized and then w washed and dried (Ref 9). See also under "Cellulose Nitration, Denitration in Vol 2, C118-R to C119-R... 

Before considering the dry spin process in a dimensional analysis, some terms have to be explained and defined. 

The irrelevance of h0 is not surprising if the solid particles are neither damaged nor compressed in the peel out process and if the capillary rise height is h0. The above pi-space should also apply for filter cakes which can be compressed to a greater extent [87]. The fact that 11) is not significant at total wetting, can only document the irrelevance of a during the dry spin process. 

The new technique of CDA sample preparation for light scattering measurements was successfully applied for industrial purposes, to develop a high-speed dry spinning process of CDA fiber 49). 

If the polyurethane molecule is allowed to form a three-dimensional structure, it becomes insoluble and neither wet nor dry spinning processes can be used. A chemical spinning process must be used in this case. The trick is to spin the isocyanate-terminated prepolymer at a stage where it forms a viscous melt, and with the jets produced in an environment that contains a chain extender. This chain extender diffuses into the fibers and reacts to couple the prepolymer molecules (Couper, 1985). 

Camille and Henry Dreyfus developed the first commercial process to manufacture cellulose acetate in 1905 and commercialized the spinning of cellulose acetate fibers in 1924 in the United States. At that time, the only other human-made fiber was viscose rayon, which was still in its early stages of commercialization. The main textile fibers were natural fibers cotton, wool, silk, and flax. Cellulose triacetate textile fiber was commercialized later in the 1950s. The tremendous technical effort by the Dreyfus Brothers resulted in more than 300 patents describing such significant inventions as the dry-spinning process and disperse dyeing. 

In the dry-spinning process, a solution of polymer is extruded through a spinneret that is mounted at the top of a heated column. As the solution is extruded in the presence of hot inert... 

The University of Florida, in collaboration with 3M, has developed a potentially lower cost, dry spun polymer-derived analogue of Hi-Nicalon fiber. It appears that this process can produce the same microstructural evolution that produeed the high-performance Nicalon/Hi-Nicalon family of SiC fibers. Processing costs may be lower because this fiber does not require a separate thermal cross-linking (cure) step. This advantage may, however, be somewhat offset by the controlled evaporation and recovery of solvent, which is inherent in the dry spinning process. 

FIGURE 4-4 Schematic illustration of the dry-spinning process. Source 3M Company... 

Films Acetone is likewise used as the solvent for commercial cast film production from CDA [43]. A schematic of the Clarifoil process to produce CDA cast film is shown in Figure 3.14. Dope preparation is similar to the dry spinning process but with the addition of adding plasticizer, normally diethyl phthalate in concentrations in the range between 10 and 25%. 

A continuous dry spinning process has been developed where a solution of polymer, water, and salt is extruded into a gaseous medium [30]. The gaseous medium removes at least 25% weight percent of the solvent from the fiber. Then the fiber is quenched in an aqueous solution. After the fiber is conditioned, the fiber is eventually drawn. 

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